Gamma radiation-induced defects, phase transformation, and color change in ZIF materials (ZIF-8 and ZIF-L) for enhanced hydrogen generation

Abstract

This study presents the effects of gamma (γ) radiation exposure on zeolitic imidazolate frameworks and elucidates the impact of irradiation on the material. Two different ZIF materials, namely, three-dimensional (3D) crystals (ZIF-8) and two-dimensional (2D) crystals (ZIF-L), were investigated. The oxidation environment of γ-radiation (1.3 kGy h⁻¹) caused the phase transformation of both ZIF-8 and ZIF-L into ZIF-L materials, creating point defects. A yellow-orange colored ZIF-L was obtained from both materials. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, diffuse reflectance spectroscopy (DRS), Tauc plots, and electrochemical measurements (cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) using Nyquist plots). γZIF-8 and γZIF-L showed broad absorption in the wavelength range of 200–600 nm with the maximum absorption at 350 nm, offering an optical bandgap of 0.6 eV. Furthermore, the particle size of pristine ZIF-L decreased from 5 μm to 0.5–1 μm after being exposed to gamma radiation. The materials before and after exposure to gamma radiation were used for hydrogen generation via the hydrolysis of sodium borohydride (NaBH₄). Gamma radiation improved the hydrogen-generation rates for both ZIF-8 and ZIF-L. The color of the materials turned lemon yellow after hydrogen generation, offering a maximum absorption at 285 nm. This observation indicates that gamma radiation caused a change in the color of ZIF materials.